The invention relates generally to methods for converting carbon and hydrocarbon cracking and apparatuses for hydrocarbon cracking. More specifically, the invention relates to methods for converting carbon into carbon oxide, and methods and apparatuses for hydrocarbon cracking, in which the build-up of coke deposits are undesirable.
In the petrochemical industry, hydrocarbons such as ethane, propane, butane, heptane, liquid petroleum gas, naphtha, and gas oil are cracked in apparatuses, in the presence of from about 30 weight percentage to about 70 weight percentage of steam, at temperatures of from about 700° C. to about 870° C. in order to produce light olefins such as ethylene and propylene. Sometimes, hydrocarbons such as bottoms from atmospheric and vacuum distillation of crude oil are cracked in apparatuses at a temperature in a range from about 480° C. to about 600° C. in the presence of about 1 wt % to about 2 wt % steam.
During hydrocarbon cracking processes, the build-up of carbonaceous deposits (i.e. coke deposits) usually happens on contact surfaces of apparatus components, for instance, inner radiant tube surfaces of furnace equipment. The inner radiant tube surfaces become gradually coated with a layer of coke which raises the radiant tube metal temperature (TMT) and increases the temperature drop through radiant coils. In addition, coke build-up adversely affects the physical characteristics of the apparatus components, such as the radiant tubes, by deteriorating mechanical properties such as stress rupture, thermal fatigue, and ductility.
In order to decoke apparatus components, the apparatus must be periodically shut down. Typically, the decoking is carried out by combustion of the coke deposits with steam/air at temperatures of up to 1000° C. Such decoking operations are required approximately every 10 to 80 days, depending on the operation mode, types of hydrocarbons, and result in production loss since hydrocarbons feeding must be stopped for such decoking operation.
A variety of methods have been considered in order to overcome the disadvantages of coke build-up on apparatus components, such as furnace tube inner surfaces. These approaches include: e.g., catalytic gasification of coke to produce carbon oxide (CO/CO2) and hydrogen. However, till now people are still seeking an effective method for the gasification of coke, i.e., converting carbon into a carbon oxide (CO and/or CO2).
Therefore, it is desirable to provide a method for converting carbon into carbon oxide and a method and an apparatus for hydrocarbon cracking, in which the build-up of coke deposits is effectively reduced/mitigated.
Carnegieite is the high-temperature form of Na[AlSiO4]-nepheline, which can be prepared by annealing nepheline beyond 1530 K (1256.85° C.) with subsequent quenching to room temperature. Intercalation of sodium oxide into Na[AlSiO4]-carnegieite to obtain compounds (Na2O)≦0.33Na[AlSiO4] has been reported in an article titled as Interstitial Cristobalite-type Compounds (Na2O)≦0.33Na[AlSiO4] and published in JOURNAL OF SOLID STATE CHEMISTRY 61, 40-46 (1986). Na8Al4Si4O18 has also been reported in Beitrage zur Beaktionsfahigkeit der silicate bei niedrigen temperaturen, II. Mitteilung., Die Strukturen Na2O-reicher carnegieite., Von Werner Borchert and Jurgen Keidel, Heidelberg, Mit 6 Textabbildungen, (Eingegangen am 17, Marz 1947). However, there seems no or few, if any, reports about how to use this kind of Na2O intercalated or rich carnegieite-like materials.